Thermal isolation for hybrid thermal detectors

Abstract

A hybrid thermal detector (10, 110) includes a focal plane array (20, 120), a thermal isolation structure (40, 140), and an integrated circuit substrate (60, 160). The focal plane array (20, 120) includes thermal sensors (30, 130). The thermal isolation structure (40, 140) includes untrimmed mesa-type formations (44, 146, 148) and mesa strip conductors (42, 142, 144) that provide thermal isolation, signal transport, and structural support of the focal plane array (20, 120) when mounted on the integrated circuit substrate (60, 160). Hybrid thermal detector (10) includes a common electrode (28) which provides a bias voltage to all thermal sensors (30). Hybrid thermal detector (110) has electrically isolated thermal sensors (130), each thermal sensor (130) is supported by mesa strip conductors (142, 144), which provide a bias voltage to and receive a signal voltage from the thermal sensor (130). To improve both pixel-substrate and inter-pixel thermal isolation, mesa strip conductors (42, 142, 144) and common electrode (28) may be formed from a thermally insulating material, such as cermet or a semiconductive material. Untrimmed mesa-type formations (44, 146, 148) may be anisotropically etched to remove excess mesa material and improve pixel-substrate thermal isolation.

What is claimed is: 
     
       1. A hybrid thermal detector comprising: at least three thermal sensors for generating a sensor signal output representative of the thermal radiation incident to the respective thermal sensor, each thermal sensor having an associated pyroelectric element;   a substrate having at least three signal contact pads for receiving the sensor signal outputs from the respective thermal sensors and at least three bias contact pads for applying bias inputs to the respective thermal sensors;   at least three pairs of mesa-type formations wherein each pair has a first mesa-type formation projecting adjacent to one of the signal contact pads of the substrate and a second mesa-type formation projecting adjacent to one of the bias contact pads;   at least three pairs of mesa strip conductors disposed between the thermal sensors and the substrate, each mesa strip conductor extending from the top of an associated mesa-type formation to a corresponding contact pad of the substrate, each mesa strip conductor formed from a single film of thermally insulating material; and   the thermal sensors being disposed over the substrate such that each thermal sensor is coupled with the corresponding bias contact pad by the respective mesa strip conductor and the sensor signal output for each thermal sensor is coupled with the corresponding signal contact pad by the respective mesa strip conductor.   
     
     
       2. The detector of claim 1, wherein the mesa strip conductors are formed from low thermal conductivity cermet having a metal concentration by weight of 70% to 90% and a corresponding ceramic concentration of weight between 30% and 10%. 
     
     
       3. The detector of claim 1, wherein the mesa strip conductors are formed from a matrix of silicon monoxide and chromium. 
     
     
       4. The detector of claim 1, wherein the mesa-type formations are substantially defined by the vertical projections of the associated mesa strip conductors on the substrate. 
     
     
       5. The detector of claim 1, further comprising: an infrared absorber layer sensitive to infrared radiation coupled to the thermal sensors.   
     
     
       6. The detector of claim 5, wherein the infrared absorber layer has at least three slots formed therein, the slots formed intermediate the thermal sensors to improve inter-pixel thermal isolation. 
     
     
       7. The detector of claim 5, wherein the infrared absorber layer has slots disposed around the entire periphery of at least one thermal sensor, thereby improving the inter-pixel thermal isolation. 
     
     
       8. The detector of claim 1, wherein each thermal sensor further comprises: an infrared absorber and reflective plate assembly having an infrared absorber layer sensitive to infrared radiation disposed on a reflective plate; and   the thermal sensor having its associated pyroelectric element formed from barium strontium titanate, the infrared absorber and reflective plate assembly coupled with one side of the pyroelectric element and a sensor signal electrode bonded to at least one mesa strip conductor and coupled with the opposite side of the pyroelectric element.